1. Field of the Invention
The field of art to which the claimed invention pertains is the treatment of sour petroleum distillates or fractions, said treatment being commonly referred to as sweetening. More specifically, the claimed invention relates to a method of treating a mercaptan containing sour petroleum distillate which comprises contacting said distillate at oxidation conditions with a catalytic composite comprising a carrier material, a metal chelate oxidation catalyst, a substituted ammonium compound, and a linear ionic compound.
2. Description of the Prior Art
Processes for the treatment of a sour petroleum distillate, wherein said distillate is treated, in the presence of an oxidizing agent at alkaline reaction conditions, with a supported metal phthalocyanine catalyst disposed as a fixed bed in a treating or reaction zone, have become well known and widely accepted in the industry. The treating process is typically designed to effect the catalytic oxidation of offensive mercaptans contained in the sour petroleum distillate with the formation of innocuous disulfides. The oxidizing agent is most often air admixed with the sour petroleum distillate to be treated. Gasoline, including natural, straight run and cracked gasolines, is the most frequently treated sour petroleum distillate. Other sour petroleum distillates include the normally gaseous petroleum fraction as well as naphtha, kerosene, jet fuel, fuel oil, lube oil, and the like.
A commonly used continuous process for treating sour petroleum distillates entails treating the distillate in contact with a metal phthalocyanine catalyst dispersed in an aqueous caustic solution to yield a doctor sweet product. The sour distillate and the catalyst-containing aqueous caustic solution provide a liquid-liquid system wherein mercaptans are converted to disulfides at the interface of the immiscible solutions in the presence of an oxidizing agent--usually air. Sour petroleum distillates containing more difficultly oxidizable mercaptans are more effectively treated in contact with a metal phthalocyanine catalyst disposed on a high surface area adsorptive support--usually a metal phthalocyanine on an activated charcoal. The distillate is treated in contact with the supported metal phthalocyanine catalyst at oxidation conditions in the presence of an alkaline agent. One such process is described in U.S. Pat. No. 2,988,500. The oxidizing agent is most often air admixed with the distillate to be treated, and the alkaline agent is most often an aqueous caustic solution charged continuously to the process or intermittently as required to maintain the catalyst in a caustic-wetted state.
The prior art suggests that a way to impove the oxidation of mercaptans contained in sour petroleum distillates is the addition of specified additives to the metal phthalocyanine solutions employed in preparing the catalytic composites. The prior art discloses that a higher activity catalytic composite results from the use of a soluble acid amide (U.S. Pat. No. 4,098,681). A catalytic composite of improved activity has also been found to result from the inclusion of a carboxylic acid in a metal phthalocyanine solution (U.S. Pat. No. 4,087,378, U.S. Pat. No. 4,107,078). Other additives to the metal phthalocyanine solution which have been disclosed as providing a catalytic composite of higher activity are polynuclear aromatic sulfonic acid (U.S. Pat. No. 4,124,531), morpholine (U.S. Pat. No. 4,142,964), and an alkanolamine hydroxide (U.S. Pat. No. 4,159,964).
The prior art does not, however, suggest that a sweetening process can be effected in the presence of a catalytic composite comprising a carrier material, a metal chelate oxidation catalyst, a substituted ammonium compound, and a linear ionic compound.
It is a broad objective of my invention to provide a novel process for treating a mercaptan-containing petroleum distillate.
In brief summary, my invention is, in one embodiment, a sweetening process, comprising contacting, in the presence of an alkaline reagent at oxidation conditions, a mercaptan-containing sour petroleum distillate with a catalytic composite comprising a carrier material, a metal chelate oxidation catalyst, a linear ionic compound, and a substituted ammonium compound.
A more specific embodiment of my invention comprises the process recited in the preceding paragraph wherein the linear ionic compound contains from about 9 to about 24 carbon atoms and has an anionic portion, wherein said anionic portion is selected from the group consisting of sulfonate, sulfate and carboxylate and the substituted ammonium compound is represented by the structural formula: ##STR1## where R is a hydrocarbon radical containing up to about 20 carbon atoms and selected from the group consisting of alkyl, cycloalkyl, aryl, alkaryl and aralkyl, R.sub.1 is a substantially straight-chain alkyl radical containing from 5 to about 20 carbon atoms, and X is an anion selected from the group consisting of halide, nitrate, nitrite, sulfate, phosphate, acetate, citrate, tartrate and hydroxide.
One of the preferred embodiments of my invention comprises the process as recited above wherein the substituted ammonium compound is dimethylbenzylalkylammonium chloride, and the metal chelate oxidation catalyst is a cobalt phthalocyanine sulfonate.
Other objects and embodiments will become apparent in the following detailed description.